Process for obtaining a tannin extract isolated from grapes, tannin extract obtained and uses thereof

Abstract

A process for obtaining a tannin extract isolated from whole grape seeds is provided. The process is performed in as a one-pot reaction and in a single extraction step, wherein the seeds are processed without grinding or milling. Also provided is a tannin extract with improved antioxidant and light fastness properties obtained from whole grape seeds that includes a mixture of tannins and non-tannins, in which the content of tannins or polyphenols is higher than 50%. Ise, the tannin extract isolated from whole grape seeds can include a coloring agent.

The invention claimed is: 
     
       1. A tannin extract obtained by a method comprising:
 (a) adding an aqueous solution of a polyphenol-solubilizing agent to whole grape seeds without grinding or milling, wherein the polyphenol-solubilizing agent is selected from the group consisting of urea, sodium hydroxide, and a compound containing an SO 3  group and is present at a concentration in the aqueous solution of 1-15% by weight with respect to the weight of the whole grape seeds; 
 (b) reacting the aqueous solution of the polyphenol-solubilizing agent and the whole grape seeds at a pressure ranging between 2.5 and 3.5 atmospheres, and a temperature ranging between 100° C. and 160° C., in a period of time ranging from 1-2 hours in an autoclave reactor; and 
 (c) recovering a liquid extract from the autoclave reactor, 
 wherein the liquid extract comprises a mixture of pure hydrolysable tannins, pure condensed tannins that include procyanidins, and non-tannins that include gallic acid, and further wherein the liquid extract has a content of tannins or polyphenols that is greater than 50%. 
 
     
     
       2. A device comprising the tannin extract of  claim 1 . 
     
     
       3. The device of  claim 2 , wherein the device comprises leather. 
     
     
       4. The device of  claim 2 , wherein the device is a food. 
     
     
       5. The device of  claim 2 , wherein the device is a cosmetic. 
     
     
       6. The device of  claim 2 , wherein the device is a drug. 
     
     
       7. A method of producing an aqueous liquid tannin extract comprising:
 (a) adding an aqueous solution of a polyphenol-solubilizing agent to whole grape seeds without grinding or milling, wherein the polyphenol-solubilizing agent is selected from the group consisting of urea, sodium hydroxide, and a compound containing an SO3 group and is present at a concentration in the aqueous solution of 1-15% by weight with respect to the weight of the whole grape seeds; 
 (b) reacting the aqueous solution of the polyphenol-solubilizing agent and the whole grape seeds at a pressure ranging between 2.5 and 3.5 atmospheres, and a temperature ranging between 100° C. and 160° C., in a period of time ranging from 1-2 hours in an autoclave reactor; and 
 (c) recovering a liquid extract from the autoclave reactor, 
 wherein the liquid extract comprises a mixture of pure hydrolysable tannins, pure condensed tannins that include procyanidins, and non-tannins that include gallic acid, and further wherein the liquid extract has a content of tannins or polyphenols that is greater than 50%. 
 
     
     
       8. The process according to  claim 7 , wherein the polyphenol-solubilising agent is urea whereby further extracting in the tannin extract an azo colouring agent free of banned aromatic amines showing a maximum at 352.8 nm, 2.70 A, measured by UV-Vis spectroscopy between 350-800 nm. 
     
     
       9. The process according to  claim 7 , wherein the concentration of the polyphenol-solubilising agent in the aqueous solution ranges between 2% and 8% by weight with respect to the weight of the whole grape seeds. 
     
     
       10. The process according to  claim 7 , wherein the weight ratio between the grape seeds and the water used to prepare the aqueous solution ranges between 0.5:1 and 1:4. 
     
     
       11. The process according to  claim 7 , wherein the extraction step is performed at a temperature ranging between 100° C. and 130° C., and a pressure ranging between 2.5 and 3.5 atmospheres. 
     
     
       12. The process according to  claim 7 , wherein, once the extraction process has been completed, the reactor is cleaned with new water that is susceptible to being reused to prepare a new aqueous solution of the polyphenol-solubilising agent. 
     
     
       13. The tannin extract according to  claim 1 , wherein the polyphenol-solubilizing agent is urea and the tannin extract further comprises an azo coloring agent free of banned aromatic amines and shows a maximum at 352.8 nm, 2.70 A, measured by UV-Vis spectroscopy between 350-800 nm. 
     
     
       14. The process of  claim 7 , further comprising concentrating the extract by evaporation, to obtain the isolated tannin extract in a concentrated form. 
     
     
       15. The process of  claim 7 , further comprising spray drying, to obtain the isolated tannin extract in the solid state.